Welcome to the latest edition of the Accretionary Wedge geoblogging carnival. We’ve been delighted by the response to our call for your favourite geological imagery, and the number of nominations we’ve received has been matched by their diversity – images have ranged from the microscopic to continental scales, from the depths of geological time to the present day, from the igneous to the sedimentary. The only way we could think of to do this smorgasboard of earth science justice was in the form of a visual dictionary, matching the images you’ve provided to the feature or process that they exemplify. Clicking on each image will allow you to see it in all its full-resolution glory at the original post, which in many cases also provides some more background on the geological feature or process depicted. Fun, pretty and at least a little bit educational – we hope you’ll have as much fun looking through our little glossary as we had putting it together.

A

Arch, natural – Formed by differential erosion at the base of a narrow ridge.

Differential weathering – divergence in the degree of weathering and erosion of different lithologies exposed to the same environment. Differential weathering is a factor in the formation of arches, buttes, and mesas, as well as steep slopes where some layers form vertical cliffs and other rock layers have subvertical exposures.

Picture: Letchworth State Park in Castille, NY, painted by Levi Wells. From John van Hoesen.

E

Exposure – the amount of geology that is exposed on the surface, and not hidden by pesky vegetation, soils, etc.

Extinction event – abrupt disappearance of species, often as a result of extreme environmental changes, which can also result in a prominent lithological boundary. Significant (mass) extinction events include:

K

L

Landslide dam – formed when a landslide blocks a river valley, these natural dams impound water upstream. Such dams can create hazards if the upstream impounded water floods property or if they suddenly overtop or breach releasing a flood wave downstream.

P

Power Law Creep – a type of deformation where small increases in applied stress leads to greatly increased strain rates. Thought to control deformation in the mantle explaining how you can get extremely rapid mantle flow around subducting slabs.

V

Volcano – an opening in the Earth’s surface through which lava, ash, or gases are erupted. Volcanoes chiefly occur in regions where rifting, subduction, or hot spots have triggered melting of the mantle.